24 ' The Colorado Experiment Station. 
irrigation, particularly the Glauber’s salt, is more than ample to 
bring about the solution of the arsenic. 
TWO KINDS OE ARSENICAL POISONING. 
So far I have not mentioned the character of this arsenical 
poisoning whether it is a general systemic poisoning or a case of 
acute irritant poisoning. That the former class of poisoning may 
occur seems very probable as in the case of one of the pear trees 
studied but all the rest of the cases with which we have met so far, 
seem clearly to belong to the latter class. The possibility of the 
occurrence of the former, however, is a matter for serious concern, 
for if the soil becomes sufficiently rich in arsenical compounds to 
enable the roots to appropriate the arsenic as they do the general 
sustenance of the tree then the poisonipg of the tree becomes a ques¬ 
tion of its ability to tolerate the poison. I fear that we have some 
c.ises in which our statement that the beginning of the trouble is at 
the crown of the tree, is not applicable, though this, as a rule, seems 
to be the case. Still it is suggestive, as elsewhere indicated, that 
often the dead roots are not as intimately connected with the af¬ 
fected areas of the crown as those which still retain a little life. 
The lead and lime with which the arsenic is combined in the 
sprays may be appropriated by the tree to its injury. The amount 
of lime, however, added to the soil as lime arsenite would be wholly 
insignificant in comparison with the lime already present in nearly 
all of the soils with which we are concerned in this bulletin unless 
it were taken up as arsenite of lime. 
There are really three substances which might act as poisons 
to the trees, namely, arsenic, lead and lime. 
ARSENICAL POISONING. 
I have already discussed the question of arsenical poisoning so 
far as the purposes of this bulletin demand. 
LEAD POISONING. 
The question of lead poisoning is a permissible one for dis¬ 
cussion, but while lead, as it was found in every sample tested for 
it, is probably present in all of the samples and may have some 
influence, the action of the arsenic appears so clearly the important 
one that the action of lead may be dismissed with this brief mention. 
THE EEEECT OE LIME. 
This question is one which cannot justly be left wholly without 
mention. As indicated above the lime and arsenic may be taken 
up in combination, or it may be simultaneously but not in com¬ 
bination and it would be difficult to distinguish their separate ac¬ 
tion. There are, however, other questions which involve the case 
